1. Field of the Invention
The present invention relates to methods for manufacturing solderable, temperable thin film tracks which are free of precious metal and which are applied to an electrically non-conducting substrate serving as a carrier in the form of an integrated film or hybrid circuit and wherein an adhesive layer is disposed between the conductive track layer and the substrate.
2. Description of the Prior Art
Conventional hybrid and integrated circuits are generally built upon an insulating substrate carrier comprised of, for example, ceramic, glass, glazed ceramic, synthetic or the like, all of which exhibit low surface roughness. Various electrical components such as resistors, capacitors, coils and conductor tracks are generated thereon according to various known methods from superimposed layers consisting of conductive material, resistance material, and/or non-conductive material as needed.
In an untempered state, tracks and contact locations comprised of copper can be easily soldered and have a better conductance than those consisting of combinations of precious metals, such as for example CuNiAu and PdAu. The adhesion of the copper layer on the substrate is, however, very poor. One solution to the problem of a lack of adhesion between the copper layer and the substrate is the application of a thin layer exhibiting good adhesion properties to the substrate carrier before application of the copper layer thereover.
In order to achieve solderable, mechanically stable and temperature resistant (up to 300.degree. C.) track systems without the use of precious metal which exhibit a low resistance, such track systems have conventionally been generated according to known methods either with thick galvanically reinforced layers comprised of, for example, copper, or by tempering a thin conductive layer in a vacuum furnace or in a protective gas atmosphere. The thin conductive layers are applied to the insulating substrate by means of vapor-deposition or sputter-deposition in the vacuum and, depending upon the use to be made of the circuit, are reinforced or strengthened by means of electrochemical precipitation. The generation of the appropriate track structure is undertaken by vapor-deposition or sputter-deposition with the use of mechanical masks or by means of known photolithographic and etching processes.
In an untempered state, the copper conductive tracks retain the characteristic of being easily soldered. At higher temperatures, beginning at approximately 250.degree. C., which occur in the stabilization of the resistance layers by temperature, a strong oxidation of the copper layer occurs. The layer of copper oxide which arises thereby does not prevent continuation of this oxidation process, and the relatively thick copper tracks in the range of, for example, 1 through 3 micrometers become throughly internally oxidized during the course of time and are no longer solderable.